The smaller tail will most likely fill out with time. Some cockerels/roosters just have smaller sickle feathers. What gives it away is the size and redness of the comb and wattles as well as the pointy hackle, saddle and sickle feathers. They also both have big feet and legs, which is a common trait of cockerels.
The boy on the left is also more white, and Golden Comet males are supposed to be, but if they aren't sex link, that wouldn't really apply. Also, they aren't 25 weeks old. Even 18 is a stretch, but could be accurate.
It is normal for an adult, mature hen to have a big comb and wattles. Not for a young female chicken, though. You most certainly have two boys.